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The mini vane is for in duct only. It is too small for a register, it would not be as accurate as a large vane. All airflow instruments, hot wire, vane, and pitot require somewhat laminar airflow to get a good measurement. In more turbulent airflow a vane is going to be more accurate then a hot wire simply due to design characteristics. If you get stuck on a box plenum, you have to measure the airflow at each of the return registers and total the airflow. The air is to turbulent to get any kind of close to accurate measurement otherwise.

The mini vane is for in duct only. It is too small for a register, it would not be as accurate as a large vane. All airflow instruments, hot wire, vane, and pitot require somewhat laminar airflow to get a good measurement. In more turbulent airflow a vane is going to be more accurate then a hot wire simply due to design characteristics. If you get stuck on a box plenum, you have to measure the airflow at each of the return registers and total the airflow. The air is to turbulent to get any kind of close to accurate measurement otherwise.

How do you get the minivane in the duct and how do you traverse the duct with it?

The main thing is to keep the main thing the main thing!

If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

I was looking at the mini vane but am leaning toward a hotwire. It just seems to me that the mini vane has to many angles to adjust to make sure the air is going through it straight. If you are off by much on your x,y,or z axis it can affect the reading. With the hotwire you can be off by 10%. If i'm wrong on this someone please enlighten me as I haven't bought one yet but am getting close.

I have a large vane that I have used but as someone said before the readings seem to vary a lot. I think part of that is because the it's so large that to get several readings sometimes your hand is blocking part of the register that your not testing and you don't always hold it correctly in relation to the flow of air from the register.

I was looking at the mini vane but am leaning toward a hotwire. It just seems to me that the mini vane has to many angles to adjust to make sure the air is going through it straight. If you are off by much on your x,y,or z axis it can affect the reading. With the hotwire you can be off by 10%. If i'm wrong on this someone please enlighten me as I haven't bought one yet but am getting close.

I have a large vane that I have used but as someone said before the readings seem to vary a lot. I think part of that is because the it's so large that to get several readings sometimes your hand is blocking part of the register that your not testing and you don't always hold it correctly in relation to the flow of air from the register.

You would be incorrect. Because a vane is directional it is more accurate. Changes in yaw and pitch of 10% will only cause an error of 3-5%. A Hotwire will indicate a false high reading in turbulent airflow because the sensor is impacted from multiple directions. Also the sensor is so small it is easily impacted by Eddie currents. A hot wire also needs to be corrected for air density to get precise results. The advantage of a Hotwire like the STA2 is the cost. The Fieldpiece gives very good results for the money. Used carefully and in a reasonable air stream you can get good results.

Also the reason for error with a large vane is typically user error, technique, and not properly correcting for use on supplies. I would not use a large vane for measuring air volume on supples but rather for porportional velocity balancing. A hood is a much better selection for air volume. For volume at a return, a vane is fine.

That brings up my next question. It seems that in the videos the readings are being taken from the return air. Is the return a better reference due to turbulence, etc?
I think the biggest 2 areas that I would need this mini vane would be in determining system airflow on changeouts and determining if a branch has enough airflow to support the additional duct that we are always asked about installing for that trouble area in the house.

The main thing is to keep the main thing the main thing!

If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!